Reactive Oxygen Species in a Non‐thermal Plasma Microjet and Water System: Generation, Conversion, and Contributions to Bacteria Inactivation—An Analysis by Electron Spin Resonance Spectroscopy

Abstract

Hydroxyl radical (•OH) and singlet oxygen (1O2) were detected by electron spin resonance (ESR) spectroscopy in a direct current He/O2 (2%) non‐thermal plasma microjet‐water system. ${}^{ \bullet }{\rm O}_{{\rm 2}}^{- } $ is shown to be the precursor of •OH. The concentrations of 1O2 and •OH are evaluated to be around 6 × 10−4 and 1.2 × 10−5 M, respectively. The survival rates of S. aureus exposed to plasma for 20 s in 1 ml H2O, SOD (100 U, for scavenging ${}^{ \bullet }{\rm O}_{{\rm 2}}^{- } $), D‐Man (0.15 M, for scavenging •OH), and L‐His (0.15 M, for scavenging •OH and 1O2) solutions were 0.7, 1.6, 13.4, and 40.9%, respectively, indicating that 1O2 contributes the most to the inactivation.

Inactivation of Candida albicans Biofilms on Polymethyl Methacrylate and Enhancement of the Drug Susceptibility by Cold Ar/O2 Plasma Jet

“…Atomic oxygen, OH radical, and strong excited nitrogen emissions detected in the plasma (Fig. 2a) are believed to play an important role to the inactivation process [46,47], which is attributed to activate oxidative stress pathway and change of the cell cycle pathway [34]. The reaction can be simulated by Fig.…”

Non-thermal plasma-activated water inactivation of food-borne pathogen on fresh produce

“…e + H2O → H + OH + e [44] e + H3O + → 2H + OH [45] OH + + O → O2 + + H [45] The results of OES indicated that excited atomic oxygen in gas plasma generated over the water, which can transfer into the liquid and be easily converted to other ROS in the liquid, such as hydroxyl radical ( • OH), singlet oxygen ( 1 O2), superoxide anion ( • O2 − ) and hydrogen peroxide (H2O2) due to its high reactivity [46]. Furthermore, three important ROS, namely, • OH, 1 O2 and • O2 − were also evidenced to exist in the water after plasma treatment by electron spin resonance (ESR) diagnosis in our earlier papers [21,47].…”

Mechanisms of Selective Antitumor Action of Cold Atmospheric Plasma‐Derived Reactive Oxygen and Nitrogen Species

“…The analysis we have presented favors singlet oxygen from CAP as the primary reaction partner for selective destruction of tumor cells. There are numerous reports of gas phase CAP generation of singlet oxygen and correlated, subsequent biological effects in adjacent liquid media …”